The present invention relates to a silver halide color photographic light-sensitive material, more specifically to a silver halide color photographic light-sensitive material of which the color reproducibility and printing suitability are kept improved against the variation of photographing conditions, such as a change in light source.
In recent years, silver halide multilayer color photographic light-sensitive materials have been significantly improved in image quality. The light-sensitive materials now on the market are excellent in graininess, sharpness and color reproducibility, which are the determinants of image quality, and, it seems that photoprints and slide films obtained from these materials almost satisfy users' requirements.
However, there is yet room for improvement in color reproducibility. Conventional light-sensitive materials are improved in the purity of color, but cannot reproduce colors that have been regarded as difficult to be reproduced by photographing.
When photographing is conducted with conventional light-sensitive materials, users are sometimes disappointed with the fact that purple and bluish purple that reflect a light of not less than 600 nm in wavelength or the colors of green family such as bluish green and yellowish green are reproduced to be colors entirely different from original ones.
Meanwhile, color reproducibility is greatly affected by the following two factors--the spectral sensitivity distribution and the inter-image effect.
In forming a silver halide color photographic light-sensitive material, it is known to add a compound capable of releasing a development inhibitor or a precursor thereof upon a coupling reaction with an oxidized product of a color developing agent (the so-called DIR compound). A development inhibitor released from such DIR compound suppresses the color development of other color-sensitive layers to cause the inter-image effect which contributes to the improvement of color reproducibility In the case of a color negative, an effect similar to the inter-image effect can be obtained by the use of a colored coupler in an amount larger than that needed to cancel an obstructive negative image formed by unnecessary absorption.
However, the use of a large amount of a colored coupler increases the minimum density of a film. The increased minimum density makes the judgment on color correction in printing extremely difficult, and eventually leads to the formation of a photoprint with deteriorated color quality. These techniques are effective only in improving color purity.
Diffusible DIR compounds have been utilized widely in recent times. A diffusible DIR compound capable of releasing a development inhibitor or its precursor of high mobility greatly contributes to the improvement of color purity. However, it is difficult to control the direction in which the inter-image effect will extend, and hence, the use of such diffusible DIR compound involves such a risk that it may change the tone of color. U.S. Pat. No. 4,725,529 contains a description as to the control of the direction of the inter-image effect.
Meanwhile, U.S. Pat. No. 3,672,898 discloses a spectral sensitivity distribution effective in suppressing the variation of color reproduction due to a change in light source.
This technique, however, is not aimed at improving the reproducibility for colors which are regarded as difficult to be reproduced. The combination of the spectral sensitivity distribution technique and the inter-image effect technique is also known. For instance, Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 034541/1986 discloses a method of improving reproducibility for colors which are difficult to be reproduced. This method, aiming at improving color reproducibility not only by the effects of blue-, green- and red-sensitive layers but also by bringing about the inter-image effect from wavelengths other than the central wavelength in the spectral sensitivity distribution of each color-sensitive layer, is considered to be effective to some extent in improving reproducibility for colors with specific tones. However, this method is accompanied by such a problem that the production cost is high due to an increased coating weight of silver and more complicated production procedures which are ascribable to the provision of an inter-image effect manifesting layer and the use of other kinds of silver halide than those employed in color-sensitive emulsion layers. The effects obtained by this method are not satisfactory.
U.S. Pat. No. 3,672,898 discloses a spectral sensitivity distribution effective in preventing color reproducibility from varying by a change in light source. In this disclosure, the spectral sensitivity distributions of the blue- and red-sensitive layers are brought into the proximity of the spectral sensitivity distribution of the green-sensitive layer, thereby to prevent color from varying against a change in light source, more specifically, to prevent the sensitivity balance of each layer from varying against a change in color temperature. In this case, by the adjacency of the spectral sensitivity distributions of three color-sensitive layers, their spectral sensitivity distributions overlap one another, thus lowering the purity of color. Such lowering of color purity can be prevented to some extent by bringing about the inter-image effect by the use of the preceding diffusible DIR compound. However, for photographing under light sources other than day light, which has been widely conducted recently, the combination of the above techniques is not effective in obtaining sufficient color reproduction.
Generally, users' attention is paid to positives, rather than negatives. Therefore, the quality of a color negative is evaluated by the quality of a positive printed on color paper.
In the case of a color negative, the imbalance of color or density can be corrected to some extent by manipulating a printer when printing on color paper, and the quality of a color negative depends on the extent to which such correction can be made. Therefore, to obtain improved image quality, a negative is required to be excellent in suitability for printing (this quality will be referred to as "printing suitability"), besides the three important factors as graininess, sharpness and color reproducibility. Laboratory examination revealed that print yield was poor in photographing under a light source other than day light (e.g., fluorescent lamp), under a mixed light source of day light and other sources than day light, or under day light but in such a condition that a specific color stands out. Improvement in printing suitability in such conditions is strongly desired.
As stated above, in spite of the efforts made by experts, none of the known techniques can improve color reproducibility, in particular, color reproducibility under various light sources other than day light which differ in color temperature.
Meanwhile, the utilization of a color photographic light sensitive material for photographing has been more diversified than ever with the spread of high-speed light-sensitive materials, throwaway cameras and large prints. The development of high-speed light-sensitive materials has permitted photographing of in-door sports, a stage drama or babies without a stroboscope. However, an image obtained without a stroboscope has poor graininess in the shadow part of a subject or in the case of underexposure, and light-sensitive materials are strongly required to be improved in this respect. Similar requirement is also being made for throwaway cameras which do not require exposure control.
Conventionally, a silver halide color photographic light-sensitive material (hereinafter often referred to as a color photographic light-sensitive material or a light-sensitive material) has been demanded to have improved sensitivity and graininess, and many proposals have been made to satisfy such demand.
For instance, British Patent No. 923,045 discloses a method of improving sensitivity without imparing graininess, in which a light-sensitive emulsion layer is divided into a high-speed emulsion layer and a low-speed emulsion layer which each contain a non-diffusible coupler, these layers form colors of substantially the same tone, and the maximum color density of the high-speed layer is adjusted to be low. This method, however, is still insufficient in respect of graininess.
U.S. Pat. No. 3,843,469 discloses a high-speed multilayer color photographic light-sensitive material with improved sensitivity, in which at least one of the red-, green- and blue-sensitive emulsion layers consists of three elemental layers. The three elemental layers (the uppermost layer, the intermediate layer and the lowermost layer) are arranged in sequence of sensitivity in such a manner that a layer of the lowest sensitivity becomes the lowermost layer. Graininess obtained by this light-sensitive material is still far from a satisfactory level.
Meanwhile, the use of two-equivalent coupler which is excellent in color forming property is known as the method of improving sharpness. German Patent No. 1121470 contains a description that sharpness can be improved by dividing each light-sensitive layer into two elemental layers and by adding a two-equivalent coupler to each elemental layer. This technique can improve sharpness to some extent, but is accompanied by significantly deteriorated graininess and increased fogging.
U.S. Pat. No. 3,516,831 discloses a light-sensitive material improved in graininess and sharpness comprising at least two emulsion layers having sensitivity to the same spectral region, in which said emulsion layer is divided into a high-speed elemental layer and a low-speed elemental layer containing a four-equivalent coupler and a two-equivalent coupler, respectively. This technique, however, cannot obtain improved sensitivity.
A technique of improving graininess by adding a DIR compound in a color photographic light-sensitive material is also known in the art. This method encounters such a problem that an increase in the amount of a DIR compound significantly lowers sensitivity and color forming property, and graininess obtained by this method is not sufficient enough to gain users' satisfaction.
Japanese Patent Examined Publication No. 15495/1974 and Japanese Patent Publication O.P.I. Publication No. 91945/1987 each disclose a technique of improving graininess by dividing at least one silver halide emulsion layer into three elemental layers (a low-speed emulsion layer, a medium-speed emulsion layer and a high-speed emulsion layer) and by controlling the maximum color density of each elemental layer delicately. Graininess obtained by this technique is still insufficient.
As is evident from the foregoing, image quality cannot be improved only by the provision of a silver halide emulsion layer of multilayer structure, and what is worse, the provision of a multilayer emulsion layer results in not only an increased production cost due to an increase in the coating amount of silver, coupler or gelatin, but also deteriorated sharpness and developability ascribable to an increased dry thickness.
The so-called "pressure fogging" may occur if the amount of gelatin contained in a light-sensitive material is decreased carelessly to solve the above problems.
Generally, a light-sensitive material is often under mechanical stresses. For instance, a negative film for photographing may be rolled up in a Patrone, be folded as it is loaded in a camera, or be pulled as it is advanced in a camera. In addition, a large mechanical stress tends to be imposed on a negative film in its manufacturing process that involves cutting and processing procedures. Such mechanical stresses, through a binder (gelatin) and a support (a plastic film), are imposed on silver halide grains, and eventually impair photographic properties.
This problem is described in detail in K. B. Mather; J. Opt. Soc. Am., 38, 1054 (1948) and P. Faelens and P. de. Smet; Sci. et. Ind. Phot., 25, No. 5, 178 (1954) and P. Faelens; J. Photo. Sci. 2, 105 (1954).
The portion of a light-sensitive material under mechanical stresses is desensitized. Such desensitization causes unnecessary sensitization and fogging, leading to a significant lowering in image quality. As the method for solving this problem, the following two are known:
(1) To add a plasticizer such as a polymer and an emulsified product; and PA1 (2) To decrease the amount ratio of a silver halide to gelatin.
These methods are aiming at preventing pressure from being applied on silver halide grains.
Regarding the method (1), as the plasticizer, British Patent No. 738,618 discloses the use of a heterocyclic compound; British Patent No. 738,637 an alkylphthalate; British Patent No 738,639 an alkylester; U.S. Pat. No. 2,260,404 a polyvalent alcohol; U.S. Pat. No. 3,121,060 a carboxyalkylcellulose; Japanese Patent O.P.I. Publication No. 5017/1974 paraffin and a carboxylate; and Japanese Patent Examined Publication No. 28086/1978 an alkylacrylate and an organic acid.
The use of a plasticizer cannot produce satisfactory results, since a certain limit has to be placed on the amount of a plasticizer to prevent the mechanical strength of an emulsion layer from lowering.
The method (2) is also defective, since an increased amount of gelatin causes various problems such as a decrease in development rate.
Besides the above methods, efforts have been made to render silver halide grains strongly resistant to mechanical stresses. For instance, Japanese Patent O.P.I. Publication Nos. 116025/1975 and 1071129/1976 each suggest the addition of iridium or thallium salts in forming silver halide grains, and Japanese Patent O.P.I. Publication Nos. 178447/1983 and 35726/1984 each disclose the use of a core/shell type emulsion. These methods can make silver halide grains resistant to pressure to some extent, but are not yet satisfactory. Today, there is a strong demand for a color photographic light-sensitive material improved not only in image quality but also in resistance to pressure.
A silver halide photographic light-sensitive material is required to be improved in various respects, such as sensitivity, image quality and gradation. Fogging, storage and processing stabilities are also important factors determining the quality of a light-sensitive material, and significant improvement in these points has been demanded in recent years. However, there is not yet a method for simultaneously improving fogging property, storageability and processing stability without lowering sensitivity.
Various techniques have been employed for sensitizing a silver halide light-sensitive material. The examples include spectral sensitization in which a sensitizing dye is used; noble metal sensitization in which a salt of a noble metal such as gold, platinum and iridium is used; sulfur sensitization in which active-gelatin, sodium thiosulfate, thioacetamide or allylisothiourea is used; selenium sensitization in which colloidal selenium or selenourea is used; reduction sensitization in which a monovalent salt of tin, a polyamine or a hydrazine derivative is used; and development acceleration in which a polonium salt of nitrogen, phosphor and sulfur or a polyalkylene glycol is used.
In the photographic industry, these techniques are appropriately combined according to purpose to obtain an intended silver halide photographic light-sensitive material. However, even when combined, these techniques are still insufficient for improving processing stability (stability against fluctuations in processing conditions) and storageability, in particular, storageability at a high temperature or a high humidity.
To improve sensitivity, Japanese Patent O.P.I. Publication Nos. 138538/1985, 143331/1985, 99433/1984 and 35726/1984, and U.S. Pat. No. 4,444,877 each disclose the use of a silver halide emulsion comprising monodispersed, tabular core/shell type grains. In this disclosure, elaboration is made in the process of forcing a latent image, so that light absorbed in the core of a silver halide grain can be effectively transformed to a development nucleous. This technique, however, is defective in storage stability.
To overcome this defect, the addition of various antifoggants was proposed. U.S. Pat. Nos. 1,758,576, 2,304,962, 2,697,040, 2,697,099, 2,824,001, 2,476,536, 2,843,491, 3,251,691, British Patent Nos. 403,789 and 893,428 and Japanese Patent Examined Publication No. 9939/1983 each disclose the addition of a mercapto compound as the antifoggant. A mercapto compound, though effective in suppressing fogging, significantly lowers sensitivity. In addition, sensitivity and fogging property of a light-sensitive material containing such mercapto compound tend to deteriorate with the lapse of time.
As the method for obtaining a photographic light-sensitive material improved in both sensitivity and image quality, Japanese Patent O.P.I. Publication No. 113934/1983 discloses the use of a silver halide emulsion comprising tabular silver halide grains with an average aspect ratio of not less than 8. However, it is extremely difficult to obtain desired gradation by using this emulsion, since the development activity of tabular grains with a high aspect ratio is too high due to the morphological properties, regardless the average silver iodide content of the grains. In addition, a light-sensitive material prepared from this emulsion is insufficient in processing stability.
Meanwhile, for the improvement of developability, Japanese Patent O.P.I. Publication No. 156059/1985 discloses the provision of a layer containing silver halide grains which are substantially not sensitive to light between two silver halide light-sensitive emulsion layers differing in light sensitivity. Japanese Patent O.P.I. Publication No. 128429/1985 discloses the addition of non-light-sensitive silver halide grains to a silver halide emulsion layer that is most distant from the support, which is aimed at preventing a light-sensitive material from being affected by fluctuations in processing conditions.
These techniques are still insufficient to improve processing stability.
Further, with the spread of small-sized compact laboratories (development apparatus), quality deterioration and heterogeneity of a processing liquid has attracted users' attention as the problems that need urgent solution. The heterogeneity of a processing liquid, which is caused by insufficient stirring, results in considerable variance in photographic properties.